Manufacture of artificial fibers



Patented June 28, 1949 MANUFACTURE OF ARTIFICIAL FIBERS Edward TerryCline, Wilmington, Del., asslgnor to E. I. du Pont de Nemours & Company,Wilmington, DeL, a corporation of Delaware No Drawing. ApplicationJanuary 3, 1947,

j Serial No. 720,099

Claims.

ironabie fabrics where resistance to heat is necessary. Filaments havebeen prepared by the dry-spinning of aqueous solutions such asby therapid evaporation of the aqueous solvent when a fine stream of theaqueous polymer solution is injected into a heated chamber. However, forsuch advantages as uniformity, ease of spinning yarns of high denienandinexpensive mechanical equipment requirements, wet spinning of aqueoussolutions is preferable. This involves injecting an aqueous solution ofthe polymer into a coagulating bath. This method, however, has beenaccompanied by a serious disadvantage in that when the fibers areprepared by spinning an aqueous solution of the polymer into a saturatedaqueous solution of an inorganic salt such as NaHzPOr to coagulate thefiber, considerable 'difflculty is encountered in removing the salt fromthe fiber. Water is the best solvent for the salt.

. However, in view of the water sensitivity of thehydroxyl-containingpolymer, an aqueous wash to remove the salt tends todissolve the fibers and they become tacky when the salt concentration inthe water becomes low. After the fibers have been allowed to dry, theyare found to be stuck together and therefore unusable.-

A method for removing salts has been shown in U. S. Patent 2,388,325 inwhich water-organic solvent mixtures such as a 1:1 mixture of water andacetone, are used to remove salts from polyvinyl alcohol structuresfreshly precipitated from aqueous inorganic salt solutions withoutinjurious effect. Such a method is expensive and the aqueous organicsolution is less effective than water to extract water-soluble salts inview of the low solubility of the coagulating bath salts in organicsolvents.

An object of this invention is an improved process for the removal ofinorganic salts from coagulated hydroxyl-containing polymer structureswhich are obtained by injection of the polymer in a salt-containingcoagulating bath. Otherobiects will appear hereinafter.

The above objects are accomplished by a procedure more particularlydescribed below which comprises drawing under tension the wet spunfilaments of a synthetic linear hydroxylated polymer. having at leastone alcoholic hydroxyl group per 2.5 carbons and not more than onehydroxyl per two carbons of the polymeric chain, holding the filamentsat a length of at least twice their original length, washing with waterwhile the filaments are held at at least twice their original length toremove the coagulating bath salts from the filaments, and drying whileso maintained.

The terms original or initial length as empolyed herein mean the lengthafter coagulation of the filaments. -When no rollers or other tensioningdevices are employed in the coagulating bath, this length is that of theyarn as it leaves the bath. When yarn driven rollers are used. in thecoagulating bath, this length is that of the yarn at the time itencounters the first coagulating bath roller.

The following examples in which the parts given are by weight furtherillustrate this invention.

EXAMPLE I An aqueous solution containing 15% of a hydrolyzedethylene/vinyl acetate interpolymer containing about 5% ethylenein thehydrolyzate, was extruded by means of a gear pump through a multiholeviscose rayon type spinneret into a coagulating bath containing 45%monosodium dihydogen phosphate and 0.05% Retarder LA (20%octadecyltrimethylammoniurn bromide). From the coagulating bath the yarnwas led to a positively driven Godet, a six inch diameter glass wheelfitted with an idler roller so that several yarn wraps could be takenaround the wheel to avoid slippage. The yarn was then led through air toa positively driven wind up bobbin. By adjusting the speeds ofthevarious drives, the yarn could be stretched in controllable amountseither in the coagulating bath or in air between the Godet and wind upor both. It was found preferable to pass the yarn in the coagulatin batharound one or more rollers mounted on vertical posts in the bath beforethe yarn was led to the Godet or directly to the wind up.

During the course of the spinning, some of the yarns were subjected tovarious degrees of stretch in the coagulating bath as calculated fromthe speed of the yarn as it left the bath and the peripheral speed ofthe first roller in the'bath. Others were stretched only slightly in thebath but were stretched various degrees in air between the Godet andwind up. Where yarn driven rollers were used in the coagulating bath,the total stretch appliedto the yarn 'w...

Q calculated from the peripheral speed of the first bath roller and thespeed of the wind up bobbin.

Where no rollers were used in the coagulating bath, thetotal stretch wascalculatedfrom the peripheral speed 'oi the'Godet wheel and the speed ofthe wind up bobbin. These'calculations extent in' these regions as aresultfof friction between the yarn'and the bath or, any stationaryobject which the .yarn may touch suchfas a convergence guide. Inpractice; however, this? stretch is relati ely insignificant in view ofthe fact-that theorie tation of the yarn atthis stage is low as evidenti'rommeasurement of its orientation number as defined in the followingparagraph. A coagulating bath temperature of 60 0.. was used duringpart. thespinning. For each resistant to water so that they could bewashed with water and dried without becoming stuck together. Likewisethe yarns collected below a given wind up tension or below'a givenorientation number were stuck whereas those col1ected abovethis criticalwind up tension orzorientation number were not stuck qwashingand dry-i jing of theseyarns was carried out" at constant "yarn I length; on' the-wind up bobbins; g- If 1 the 1 I yarns are removed i'rorn'the' bobbinsand allowed to "relax completely "during washing .and*drying, j a v asin 'a skeinfthey will shrinirjfreely, l'ose orienta- V tion. and become's'tuck; Itiwas: i'oundthat' the place at which the stretchis appliedduring-spin ,ning, i. e; in the-coagulatingfbath' or.in' air out- I sidethecoa'gulating'bathj isimmaterialin regard to washability. Typicalresults obtained in this spinning are shown in'the following tables.

condition used. the tension on the yarn justbefore the wind up bobbinwas measured in grams and later calculated in terms of g. p. d. (gramsper denier). After each bobbin of yarn had been collected, it was washedin running tap water until the coagulating bath salts were substantiallyremoved; It was then allowed to dry in air and the condition'oi theyarn, i. e., whether stuck or free, was observed. Free yarns weretwisted on a conventional ring twister. Short lengths of the stuck yarnswere unwound laboriously by hand during which many of the individualfilaments were broken. The orientation numbers of the yarns were thendetermined by means of X-rays.

Orientation isdetermined by passing a collimated beam ofcopper filteredX-radiation through a bundle approximately 1mm; thick of parallel fibersonto a photographic plate during one hour with a distance of 5 cm.between the fiber specimen and the plate. The Phillips Metalix tube usedis supplied with a 19 milliampere current at 35 kilovolts. Thecollimation is effected by two 25-mil diameter pinholes intensities atthe equator of. the picture to that I at 90 degrees from the equator forthe inner and outer rings. numbers. Thus an orientation number of onedenotes that the specimen shows no orientation whereas ratiosprogressively greater. than one denote progressively higher degrees oforient-a tion. The orientation'numbers are expressed as 01 for the innerring and O: for the outer ring of the X-ray diifraction pattern. Ofthese the O2 orientation number is more accurate and.

reproducible. These values "are given in the examples.

The ratios are called orientation It was found that if the yarns werearranged VT in order of increasing amount; of total stretch,

they were also in order of increasing orientationnumber and increasingwind. up tension as ex pressed in, grams per-denier. The yarns. col Ilected below a totalstretchzof' about'100% of their original length werestuck whereas .those collected above this total stretch weresufiicientiy I yarns. The maximum'pos'siblestretch was aping. stretchand windiup tension, alsowere in orderof increasing orientation numbers.Thus.

'-Tablel Amount Yarn I Stretch'in- I I I Total 'Washedand Dried CStretch Yarn Condition 0 A|r I Percent Percent Percent 29 0 29 'Badlgstuck. 57 0 57 0.

6 61 70 D0. 72 0 72 Partly stuck. 78 0 78 Do. 0 90 I Do. m4 0 104 Free.

6 101 112 Do. 115 0 115 Do. 124 0 124 Do. 6 230 I 258 D0. 422 o 422 Do.

Table II Amount Yarn Stretched Windup Washed and Orien- Tensioln,Dcrieddiarm gititgl Cong g. p. on: on o. a Bath Per- Percent. rent 6. I28 6 61' 25 0 115 0 78 -0 222 0 104 0 6 138 The critical wind uptension'and'ba orientation number (ratio of X-ray intensity at theequator to that at the pole for the outer interference ring) for thisyarn may beseen to. lie between 0.05 and 0.07 g. p. d. and between 2.4and 2.8 respectively.

20.9 centipoises (4% aqueoussolution) was spun in a manner similar tothat described in Example I. For most of theyarns collected, practicallyall of the stretching was done in air between the I Godet and wind up.In order to avoid sticking during washing and drying it was necessary toapply a total stretch of abo'ut190% to these proximately 400%. .As wasthe case in Example I, the yarns when" arranged in orderv ofincreas- 5for the polyvinyl alcohol yarns, it was necessary that the total stretchbe higher (correspondingly, a higher wind up tension with higherorientation number) to permit washing and drying without sticking thanin the case of the hydrolyzed ethylene/vinyl acetate interpolymer yarnsdescribed in Example I. It is therefore evident that polyvinyl alcoholis more water sensitive than hydrolyzed ethylene/vinyl acetateinterpolymers. Typical results obtained in this spinning are shown inthe following tables.

Table III Amount Yarn Washed Stretch in- Total and Dried Stretch gg 3Air tion Bath Per cent Per cent Per cent 15 59 83 Stuck 16 87 no Do. f16 111 144 D0. 16 139 176 Do. 6 180 196 Free. 16 106 208 Do. 16 194 240Do. 267 86 Do. ii 207 308 Do.

Table IV Amount Yarn strewn Wind Up Washed and Orienta- Tension, DriedYarn, tion g. p. (1. Condition No. 0: Coag. Bath Per cm! Per cent 16 1110.12 Stuck 3. 7 16 139 .15 ..do 4.6 16 166 .21 Free 5. 5 l6 194 .30 do6.3 5 267 .87 do 8.1

The critical wind up tension and O2 orientation number for this yarn maybe seen to lie between 0.15 and 0.21 g. p. d. and between 4.6 and 5.5respectively.

The ethylene present in the hydrolyzed ethylens/vinyl acetateinterpolymer appears to be responsible for its greater water resistanceover polyvinyl alcohol. To avoid sticking in a bobbin process, the totalstretch for polyvinyl alcohol is at least 190% and for a hydrolyzedvinyl acetate interpolymer containing 5% ethylene is 100%. Each per centof ethylene introduced lowers the amount of total stretch by 18 from the190%. correspondingly, if the upper limits of the critical ranges ofwind up tension and O2 orientation number given in Examples I and II aretaken as the critical points, then each percent of ethylene introducedlowers the wind up tension about 0.03 g. p. d. and the O2 orientationnumber by about 0.5 without encountering sticking in the washed anddried yarn. This is illustrated in the following table. 1

, Table V Exmu 111 An aqueous solution containing 7% ethanol and i 15.4%of hydrolyzed ethylene/vinyl acetate interpolymer containing 5% ethylenewas spun in a' manner similar to that described in Example I. Thespinning solution was delivered through a hole spinneret at a rate of 3cc. a minute. In the coagulating bath, which was maintained at roomtemperature, the yarn was passed around 2 rollers such that the lengthof yarn travel in the bath was about sixty inches. The yarn was then ledto a Godet wheel operating at a peripheral speed of 380 inches perminute. It was then led thru air to the wind up bobbin, operating at aperipheral speed of 1380 inches per minute, such that it was stretchedin air 263%. (or a draw ratio of 3.63/1). The wind up tension was 0.58g. p.. d. Following washing and drying of the yarn, the filaments wereobserved not to be stuck.

EXAMPLE IV An aqueous solution containing 7% ethanol and 12.5% of highviscosity, fully hydrolyzed PVA (polyvinyl alcohol) having a viscosityof 51 centipoises (4% solution in water was spun in a manner similar tothat described in Example III. The spinning solution was delivered tothe spinneret at a rate of 4.5 cc. per minute. Following passage aroundtwo rollers in the coagulating bath, the yarn was led to a Godet wheeloperating at a peripheral speed of 285 inches per minute. From the Godetthe yarn was led to the wind up bobbin operating at a peripheral speedof 1040 inches per minute such that it was stretched in air 265%. Thewind up tension was 0.48 g. p. d. Following washing and drying the yarncould be unwound readily and the filaments were not stuck together.

EXAMPLE V EXAMPLE VI An aqueous solution containing 7.3% ethanolv i and15.4% of a hydrolyzed ethylene/vinyl acetate interpolymer containingabout 5% ethylene was spun in a manner similar to that described inExample I except that a. boiling aqueous bath containing 20% urea wasused between the Godet and the wind up such that theyarn passed thruthis solution while it was being stretched between the Godet and windup. Most of the yarn was collected at a total stretch of520%. Themaximum possible stretch was 600%. The water washed and dried yarn wasnot stuck.

EXAMPLE V'II the Godet wheel the yarn was led to a positively drivendraw roll and thence to a wind up bobbin.

The wind up bobbin was operated at a lower at'the first coagulating bathroller in spltefof 1 'the ffollowinggtable.

several different conditionsof stretch areflshown scribed in u. s.Patent 2,386,347. These polythe fact that the yarn was actuallystretched mo're.

' than this prior toits relaxationbetweenthedraw i mu and the wind upbobbin. Following'winding the yarn was washed with wa'ter, allowed todry in I air and; twisted. The results on yarns spun under piricalformula: I

- (crnoagcirnomy.(oimoa z where R is an acyl radical of an organicmonocarboxylic acid, preferably acetyl and the ratio of 1/ to z is atleast4-to 1 (i. e., 80%hydrolyzed) and preferably substantiallycompletely hydrolyzed, For polyvinyl alcohol, at is zero while for theethylene inter-polymers, the ratio of y+z to a:

is usually within the range of 6:1 to 50:1 and is preferably 6 :1 to :1since the fibers from the latter polymers have better properties.

i.:.e., "by' stretching them and'then relaxing them controlled amountsbefore windin must be given a somewhat higher total stretch than yarnsspun by the bobbinprocess without relaxation'as 'de- Iscribedin'previous examples. Thus the total net stretch required toavoid sticking of the polyvinyl alcohol fibers described in this exampleis about 220% whereas only about 190% total stretch was required for theprocess described in Example II.

It is necessary however that the polyvinyl alcohol filaments be drawn atleast 2.9 times their original length and maintained during the timethey are in. contact with water (e. g., during washing) at a length ofat least 2.9 times their I original undrawn .length. 'I f'the'filamentsare drawn more than 2.9 times their original length,

they must'be maintained during the time they are in contact with waterat their drawn length or at least 3.2 times their originallength.

The macromolecular synthetic polymers that v can be used in the processof this invention are those which haveat least one alcoholic hydroxylgroup per,2.5 carbon atoms but not more than one hydroxylyfor'two'carbon atoms of 'thechain. ;By

macromolecular ismeant an organic compound :1

" having a" degree of polymerization or anumber.

ofgrecurring units of .at 'least.100 (Staudinger,

Die Hochmolecularen Organischen Verblndungen,

1932)} Such hydroxyl-containing polymers in I clude polyvinylalcohol andhydrolyzed polyvinyl ester'polymersfland copolymers whlch have the,ratioof hydr oxyl to chain carbon previously mention'ed. {In additiontothe hydrolyzed polyvinyl esters such as polyvinyl'acetate, hydrolyzedcopolymers of vinyl esters with ethylene, vinyl chlo- V ride, vinylfluoride, vinylidene fluoride, vinylidene chloride, and otherfiber-forming polymeric material can be employed. In such copolymers,the molar ratio of vinyl ester (hydrolyzed to vinyl alcohol) to theother polymerizable compounds is preferably between 6:1 and 50:1. Ofthehydroxylated polymers those particularlypreferred are polyinyl alcoholand hydrolyzed ethylene/- vinyl ester interpolymers, containing from0.12%

a to 10.0% ethylene in the hydrolyzate. The preparation of the latterinterpolymers been: de-

. ,j s nmigg Speeds, Inches/Minute Tensions, nd; k v I i. remConditioner .Coa Godt Draw Wind At Draw At Wind "F f Bat ,7 Roll :up Rll H P'.

"i Roller i i t I Percent" 332 340 1,140 1,030 .40 .04 2101 Partlystuck. 350 311,1,384 1,103 .76 ".02. 216 -*Do. a5o .311 I 1,380 1,153-.58 .04 220 Free. .350 new 1,334, 1,210 .s4 .08 246 Do. 350 377 soo-1,280 .06 266 Do.

- g.,p. d.-granis 'per denier. 1

-It is apparent that yarns spun in this manner. The above polymers aredissolved in hot aqueous solution to an extent of between 5-and 30% .al-

though usually between 5 and 20% is'used. There may be also addedsmallamounts of water-soluble aliphatic alcohols, amines, or mercaptans.Fordiflicultly soluble polymers, mixtures of an ride, etc. Particularlydesirable in view of the better coagulating properties (effectiveness inremoving water from the polymer solution) is an 'aqueouscoagulating bathconsisting .of monosodium 'dihydrogen phosphate (NaHaPOi) l1av-- Lingfaspecific gravity of about 1.4 at 25 C.' The salt bath shouldhave a highconcentration, e. g., it should .benearly saturated with salt or ofsulficient concentration'to remove water rapidly from the aqueouspolymersolution. Cationic surface active agents'suchascetyl trimethylpyridinium bromide'in amounts of from 0.005 to 0.05% based on thewei'ght of the bath are also advantageous J in that-the filaments haveimproved properties and spinnerets are less likely to foul.- Cationicsurface active agents are described in British Pat- ..ent. 499,334.Usually the bath is saturated with respect to the surface active agent.The bath is usually maintained'at temperatures of 5 to 80 C. The drawingonstretching of the filaments 'with resulting molecular orientationalong the fiber axis is conducted under a tension which draws them to alength of at least twice their initial length and which orients thefilaments to an extent that when held at fixed length they areinsufficiently softened' by water to cause sticking of the driedfilaments. Although in allinstances .the tensionapplied' draws them, toa length of at least twice their initial length, or is at least 0.05gram per denier, the exact amount of orientation unecessary :will dependon the water sensitivity of the particular polymer, and theminimumtension wilLtherefore, be higher for the more water tion of fabrics,cordage, etc.

sensitive polymers. This figure can be obtained readily by trial or bythe rule given below for approximating the minimum tension that shouldbe'applied to orient the fiber so that it can be washed with water anddried. V

For a polymer represented by the empirical formula (C2H3OH)a (C2H4)b,the first member being the polyvinyl alcohol or hydrolyzed vinyl esterconstituent, the percent by weight of which is indicated by the lettera, and the second member being the ethylene constituent, the per cent byweight of which is indicated by the letter I), the minimum tension to beapplied is such that the increase in length in percent of the filamentsis equal to 190 minus the product (18)b. The tension in grams per denieris equal to 0.21 minus the product (0.03) (1)). Thus, for polyvinylalcoholitself, the tension should be such to produce an increase inlength of at least 190% or at least 0.21 gram per denier. Less tensionwith correspondingly less orientation-can be applied in the case of thehydrolyzed ethylene/vinyl ester interpolymers, but in any instance theminimum tension is such that the increase in length is at least 100% ormust exceed 0.05 gram per denier.

The maximum tension used naturally must be less than the breakingstrength of the fiber. Although tensions near the maximum may beemployed, such tensions may result in more broken filaments in the yarnthan are desired. It is preferable to operate at tensions or lengthincreases of about 75% of the maximum during the wet drawing. Afterdrying the filaments, the fibers may be further oriented by drawing atelevated temperatures to give filaments having high tensile strength.The amount of this hot drawing is inversely proportional to the amountof wet drawing done during the spinning operation.

The fibers obtained by the process of this invention are particularlyuseful for the prepara- Aftertreatments with formaldehyde or othermaterials can be applied to the fibers to further reduce their watersensitivity. In view of the electrical insulating properties ofhydrolyzed ethylene/vinyl acetate interpolymers, the fibers of suchinterpolymers may also be used in electrical insulation, e. g., for tapewinding or braiding of electrical conductors.

As many apparently widely diflerent embodiments of this invention may bemade without departing from the spirit and scope thereof, it

i is to be understood that I do not limit myself 10 to the specificembodiments thereof except as defined in the appended claims.

I claim:

1. In the process for manufacture of filaments, fibers and likestructures from a synthetic linear hydroxylated polymer wherein anaqueous solution of from 5% to 30% by weight of said polymer iscoagulated in an aqueous solution of an inorganic salt, the improvementwhich comprises drawing the wet spun filaments at least twice theirinitial length under a tension which orients the filaments to an extentsuch that they do not stick together after washing with water aloneanddrying, holding the drawn filaments under tension at least twice theiroriginal length and while the filaments are so held washing them toremove said salt with an aqueous wash which consists essentially ofwater and which causes swelling of the filaments in their undrawn andunoriented state, and then drying the filaments while so held, saidhydroxylated polymer having at least one alcoholic hydroxyl group per2.5 carbon and not more than one hydroxyl per two carbons of thepolymeric chain.

2. The process set forth in claim 1 in which said hydroxylated polymerconsists predominately of hydrolyzed polyvinyl ester.

3. The process set forth in claim 1 in which said hydroxylated polymerconsists predominately of hydrolyzed polyvinyl acetate.

4. The process set forth in claim 1 in which said hydroxylated polymeris a hydrolyzed ethylene/vinyl acetate interpolymer containing from0.12% to 10% ethylene in the hydrolyzate.

5. The process set forth in claim 1 inwhich said salt is monosodiumdihydrogen phosphate.

EDWARD TERRY CLINE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

